The reduction of hazards from chlorinated organics in contaminated groundwater has been studied by our multidisciplinary team of faculty and students from engineering, microbiology and environmental health by developing reactor-based bioremediation methods and unique anaerobic and cometabolic aerobic enrichments. Rates and extent of degradation of important chlorinated aliphatic and chlorinated aromatic toxicants have been investigated, helping to develop a practical range of anaerobic and aerobic biodegradation process applications. Cometabolic transformations of chlorinated aliphatic compounds by methanotrophs, phenol, toluene, and propane oxidizers has developed comparative rates for these communities and an understanding of metabolite toxicity and competitive inhibition effects. Anaerobic and aerobic processes have been investigated, accompanied by residual toxicity measurements using bacterial assays. The limitations of above ground reactors for treating contaminated groundwater resulting from non aqueous phase liquids (NAPLs) have become increasingly apparent. The low NAPL removal efficiency of pumping and flushing methods may require decades for site remediation. Consequently the research emphasis in the proposal has shifted to understanding biostimulation of in situ biodegradation in the near vicinity of NAPLs. A hydrogeologist is added to our team to assist in designing and using results of studies with aquifer microcosms. Molecular methods and near- microscale analyses are needed to understand the biostimulation processes that may significantly enhance dissolution and transport from NAPLs. Emphasis is being shifted in microbiological studies to development and use of molecular probes with a post-doctoral position to assist in this work. The broad objectives of the project are to continue to study the anaerobic and aerobic microbial enrichments that are capable of bioremediation of chlorinated organic compounds and to study their biostimulation in the near vicinity of NAPLs. Enriched cultures and isolates will be studied to investigate microbiological characteristics and engineering applications. The in situ studies require development of aquifer microcosms to simulate subsurface bioremediation near NAPLs and the development of sophisticated tools for sampling and understanding the chemical and microbiological responses to engineering variables. Biological kinetics, enrichment development, and aquifer microcosm testing will be done at room temperatures, closer to groundwater conditions than in our previous work. Kinetic modeling of microbial activity will continue, but a greater modeling activity will focus on the t transport and biodegradation in porous media with biostimulation and groundwater flow. The modeling will be used to design microcosm studies, then interpreting and simulating their results and extrapolating the results to field scale in situ bioremediation. This work will provide strong, continuing collaboration among faculty and students in engineering, microbiology and health sciences.